Once-through steam generator for use at oilfield operation site, and method

ABSTRACT

A once-through steam generator for use at an oilfield operation site includes: a control module having an enclosure including controls for operating the steam generator, a radiant module including a radiant chamber, and a convective module including an economizer heat exchanger. The enclosure is erected prior to transportation to the operation site.

FIELD OF THE INVENTION

The subject application generally relates to steam generation for oilfield operations, and in particular to a once-through steam generator for use at an oilfield operation site, and a method.

BACKGROUND OF THE INVENTION

In the field of enhanced oil recovery, steam generators are used to generate high pressure steam for injection into underground oil reservoirs for recovery of heavy crude oil. In particular, the high pressure steam is injected into a first horizontal wellbore drilled into an oil reservoir to heat the oil and to reduce its viscosity. The heated oil flows downward by gravity and enters a second horizontal wellbore situated below the first wellbore, where it is pumped to the surface. This approach is referred to as steam-assisted gravity drainage (SAGD).

A commonly-used type of steam generator in SAGD systems is the once-through steam generator (OTSG), which comprises a feed water circuit that follows a continuous, serpentine path through a radiant chamber into which heat energy is directed. The heat energy converts the water into high pressure steam as it passes through the circuit.

Once-through steam generators have been previously described. For example, U.S. Patent Application Publication No. 2014/0262257 to Costanzo et al. describes a small supercritical OTSG that includes a radiant section with a furnace coil, and a convection section downstream of the radiant section that includes a superheater which is fluidically connected to the furnace coil. The OTSG may optionally be devoid of a steam separator. An economizer can also be included downstream of the superheater. Supercritical steam can be generated using the OTSG for use, among other things, in enhanced oil recovery applications.

U.S. Pat. No. 8,951,392 to James describes a modular portable evaporator system for use in steam-assisted gravity drainage (SAGD) systems having an evaporator, with a sump comprising an oil skimming weir, a short tube vertical heat exchanger including an outer shell containing short tubes provided for lower water circulation rate. The system also has, external to the evaporator, a compressor compressing evaporated steam from the tube-side of the heat exchanger and routing to the shell side of the same exchanger, a distillate tank to collect hot distilled water, a recirculation pump to introduce liquids from the sump into the heat exchanger and an external demister protecting the compressor from liquid impurities. The evaporator receives produced water from the process into the sump and provides cleaned hot water to the boiler.

Improvements are generally desired. It is therefore at least an object to provide a novel once-through steam generator for use at an oilfield operation site, and a method.

SUMMARY OF THE INVENTION

It should be appreciated that this summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to be used to limit the scope of the claimed subject matter.

Accordingly, in one aspect there is provided a once-through steam generator for use at an oilfield operation site, the steam generator comprising: a control module having an enclosure comprising controls for operating the steam generator, the enclosure being erected prior to transportation to the operation site; a radiant module comprising a radiant chamber; and a convective module comprising an economizer heat exchanger.

The radiant chamber may have a burner installed at an end thereof. The enclosure may be configured to accommodate the burner. The burner may be configured to provide a heat transfer of between about 80 million Btu/h and about 200 million Btu/h.

The radiant module may further comprise at least one water conduit and at least one steam conduit, said conduits being external to the radiant chamber. One or more of the conduits may comprise: an electrical heating element disposed thereon, and a thermal insulation layer covering the conduit and the electrical heating element.

The control module and the radiant module may each be supported by a respective steel frame. Each steel frame may be configured to be installed on a plurality of steel piles. Each of the control module and the radiant module may be installed on the respective steel frame prior to delivery to the operation site.

The enclosure may have an insulated interior sized to accommodate at least one worker.

In another aspect, there is provided a method of installing a once-through steam generator at an oilfield operation site, the method comprising: providing each of: a control module having an enclosure comprising controls for operating the steam generator, the enclosure being erected prior to transportation to the operation site, a radiant module comprising a radiant chamber, and a convective module comprising an economizer heat exchanger; and installing the control module, the radiant module and the convective module at the operation site.

The providing may further comprise: transporting each of the control module, the radiant module and the convective module to the operation site. The method may further comprise, prior to said transporting: testing said controls for operating the steam generator.

The method may further comprise, prior to said installing: forming a foundation in ground at the operation site. The foundation may comprise an array of steel piles.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described more fully with reference to the accompanying drawings in which:

FIG. 1 is a side view of a steam-assisted gravity drainage (SAGD) system comprising a once-through steam generator;

FIGS. 2A to 2D are isometric, elevation, plan and rear views, respectively, of the steam generator of FIG. 1;

FIGS. 3A to 3D are isometric, plan and side elevation views of a radiant module forming part of the steam generator of FIG. 1;

FIG. 4 is a sectional view of a radiant chamber forming part of the radiant module of FIGS. 3A to 3D;

FIGS. 5A and 5B are isometric and plan views, respectively, of an evaporator coil forming part of the radiant chamber of FIG. 4;

FIG. 6 is an isometric view of a skid forming part of the radiant module of FIGS. 3A to 3D;

FIGS. 7A to 7G are isometric, plan, front, rear, side elevational and sectional views of a control module forming part of the steam generator of FIG. 1;

FIG. 8 is an isometric view of a skid forming part of the control module of FIGS. 7A to 7G;

FIGS. 9A and 9B are sectional end and sectional side views, respectively, of a portion of a steam output line forming part the radiant module of FIGS. 3A to 3D;

FIG. 10 is an isometric view of the steam generator of FIG. 1, installed on a foundation at an operation site; and

FIG. 11 shows a prior art enclosure partially surrounding a pair of prior art once-through steam generators.

DETAILED DESCRIPTION OF EMBODIMENTS

The foregoing summary, as well as the following detailed description of certain examples will be better understood when read in conjunction with the appended drawings. As used herein, an element or feature introduced in the singular and preceded by the word “a” or “an” should be understood as not necessarily excluding the plural of the elements or features. Further, references to “one example” or “one embodiment” are not intended to be interpreted as excluding the existence of additional examples or embodiments that also incorporate the described elements or features. Moreover, unless explicitly stated to the contrary, examples or embodiments “comprising” or “having” or “including” an element or feature or a plurality of elements or features having a particular property may include additional elements or features not having that property. Also, it will be appreciated that the terms “comprises”, “has”, “includes” means “including by not limited to” and the terms “comprising”, “having” and “including” have equivalent meanings.

As used herein, the term “and/or” can include any and all combinations of one or more of the associated listed elements or features.

It will be understood that when an element or feature is referred to as being “on”, “attached” to, “connected” to, “coupled” with, “contacting”, etc. another element or feature, that element or feature can be directly on, attached to, connected to, coupled with or contacting the other element or feature or intervening elements may also be present. In contrast, when an element or feature is referred to as being, for example, “directly on”, “directly attached” to, “directly connected” to, “directly coupled” with or “directly contacting” another element of feature, there are no intervening elements or features present.

It will be understood that spatially relative terms, such as “under”, “below”, “lower”, “over”, “above”, “upper”, “front”, “back” and the like, may be used herein for ease of description to describe the relationship of an element or feature to another element or feature as illustrated in the figures. The spatially relative terms can however, encompass different orientations in use or operation in addition to the orientation depicted in the figures.

Turning now to FIG. 1, a steam-assisted gravity drainage (SAGD) system is shown, and is generally indicated by reference numeral 20. SAGD system 20 comprises a once-through steam generator (OTSG) 22 installed at an operation site 24 on ground surface that is generally proximate an underground oil reservoir 26. The steam generator 22 is configured to generate high pressure steam for injection into the oil reservoir 26 for recovery of heavy crude oil. The SAGD system 20 has a feed water supply 28, which provides water to the steam generator 22 for generating a supply 32 of high pressure steam. The high pressure steam is conveyed to a steam injection wellhead 34, which pumps the high pressure steam into the ground via a first horizontal wellbore 36 located in in the vicinity of the oil reservoir 26. Steam flux 38 exits the first horizontal wellbore 36 and heats heavy crude oil in the oil reservoir 26, thereby rendering the heavy crude oil less viscous. A mixed flux 42 of heavy crude oil and water flows downward by gravity, and enters a second horizontal wellbore 38 located below the first horizontal wellbore 44, from which it is pumped to the surface by a recovery wellhead 46. The recovery wellhead 46 provides an output 48 comprising the mixture of heavy crude oil and water for subsequent separation and processing.

The steam generator 22 may be better seen in FIGS. 2 to 10. The steam generator 22 has a modular design, and comprises a control module 52, a radiant module 54, and a convective module 56. Each of the control module 52, the radiant module 54, and the convective module 56 is fabricated separately at a manufacturing site (not shown) distant from the operation site 24, and is transported separately in a prefabricated state from the manufacturing site for installation at the operation site 24.

The control module 52 comprises an enclosure 60 in the form of an insulated building that is supported by a skid 64 in the form of a steel frame. The steel frame comprises a plurality of steel beams that are joined by one or more of bolts, rivets and welds to provide the skid 64. The enclosure 60 is erected prior to transportation to the operating site 24, and defines an insulated interior space 66 that is accessible to workers for accessing controls and instruments associated with operation of the steam generator 22.

The control module 52 comprises a main feed water supply line 68, which conveys water from the feed water supply 28 to the radiant module 54. The control module 52 also comprises a glycol supply line 72 and a glycol return line 74, which convey glycol to and from a heater 76 for heating the interior space 66, a pressurized air line 78 for supplying pressurized air to activate the controls and instruments of the enclosure 60, and a cooling water supply line 82 and a cooling water return line 84, which convey water to and from a steam testing station 86 for cooling steam samples for testing. The control module 52 further comprises a fuel gas supply line 88, which conveys fuel gas from a fuel gas source (not shown) to a burner 90 for combustion. The control module 52 also comprises an air preheater 92, a preheated air duct 94 and a preheated air blower 96, which are configured to provide heated air to the burner 90, where it is combined with the fuel gas and burned to yield a heated flux including heat energy and combustion products. In this embodiment, the burner 90 is sized to provide a heat transfer of between about 80 million Btu/h and about 200 million Btu/h. The air preheater 92, the preheated air duct 94 and the preheated air blower 96 are positioned on an exterior platform 98 supported by the skid 64, external to the enclosure 60.

In the embodiment shown, the enclosure 60 has a removable panel 102 disposed on a wall facing the radiant module 54. The removable panel 102 is configured to be removed to allow the burner 90 to be accommodated in an area 104 of the interior space 66, upon installation of the control module 52 and the radiant module 54 at the operation site 24.

The radiant module 54 comprises an elongate radiant chamber 106 that is supported by a skid 108 in the form of a steel frame. The steel frame comprises a plurality of steel beams that are joined by one or more of bolts, rivets and welds to provide the skid 108. The burner 90 is mounted at a first end of the radiant chamber 106, and is configured to direct the heated flux through the interior of radiant chamber 106 toward the convective module 56. The radiant chamber 106 comprises a cylindrical housing 112 that surrounds an annular evaporator circuit 114 that extends generally the length of the radiant chamber 106. The annular evaporator circuit 114 comprises a pair of tubes 116 and 118 that are arranged in a serpentine manner within an annular volume to define a longitudinal passage 122, through which the heated flux flows. The radiant chamber 106 has an exhaust duct 124 at a second end thereof, which is configured to convey the heated flux to the convective module 56.

The radiant module 54 comprises a main feed water supply line 128 exterior to the radiant chamber 106, which is configured to be connected to the main feed water supply line 68 of the control module 52. The main feed water supply line 128 splits into a first feed water supply line 132 and a second feed water supply line 134. Each of the first and second feed water supply lines 132 and 134 is configured to be connected to a respective one (1) of two (2) economizer water circuits (not shown) forming part of an economizer heat exchanger (not shown) housed in the interior of the convective module 56. As will be understood, heated flux flowing from the radiant chamber 106 into the convective module 56 passes over the economizer water circuits, thereby preheating the water. As will be understood, splitting the feed water into first and second feed water supply lines 132 and 134 increases the surface area exposed to the heated flux, and thereby increases the heat transfer efficiency of both the radiant module 54 and the convective module 56.

The convective module 56 comprises an enclosure 136 that is in fluid communication with the exhaust duct 124 of the radiant chamber 54. As noted above, the interior of the enclosure 136 houses the economizer heat exchanger, which is configured to preheat water flowing through the first and second feed water supply lines 132 and 134 using the heated flux flowing from the radiant chamber 106. The enclosure 136 is also in fluid communication with a stack 138, which is configured to discharge the heated flux to atmosphere.

Turning again to the radiant module 54, the radiant module 54 comprises a first preheated water line 142 and a second preheated water line 144, each of which has a first end that is configured to be connected to a respective one of the economizer water circuits arranged in the enclosure 136 of the convective module 56. Second ends of the first and second preheated water lines 142 and 144 are connected to inputs 116 a and 118 a of the tubes 116 and 118 of the annular evaporator circuit 114, and each convey preheated water into the radiant chamber 106, in which the preheated water flowing therethrough is converted to high pressure steam.

The radiant module 54 further comprises a first steam output line 152 and a second steam output line 154, which are connected to outputs 116 b and 118 b of the annular evaporator circuit 114 and which each convey high pressure steam generated in the radiant chamber 106. The first and second steam output lines 152 and 154 are combined into a single steam output line 156, which is configured to be connected to a main steam line 158 of the control module 52.

At least some of the external water lines and steam lines of the control module 52 and the radiant module 54 are heated and insulated, or “winterized”, to provide protection against freezing. For example, FIGS. 9A and 9B show a portion of the steam output line 156, which comprises a conduit in the form of a pipe 158 through which the high pressure steam is conveyed, electric heat tracing in the form of one or more electrical heating elements 162 fastened to an outer surface of the pipe by bands 164, and a thermal insulation layer 166 covering the pipe 158 and the one or more electrical heating elements 162 and the bands 164. In the example shown, there are three (3) electrical heating elements 162 fastened to the pipe 158, and the bands 164 are segments of fiberglass tape; however other suitable fasteners may alternatively be used. In this embodiment, each of the main feed water supply line 128, the first and second feed water supply lines 132 and 134, the first and second preheated water lines 142 and 144, the first and second steam output lines 152 and 154, the steam output line 156, and the main steam line 158, are “winterized” in the above described manner. Further, in this embodiment, each of the main feed water supply line 128, a lower portion of each of the first and second feed water supply lines 132 and 134, a lower portion of each of the first and second preheated water lines 142 and 144, the first and second steam output lines 152 and 154, the steam output line 156, and the main steam line 158 are “winterized” in the above described manner at the manufacturing site, prior to transportation to the operation site 24.

Returning to the control module 52, the main steam line 158 extends into the interior space 66 of the enclosure 60, and is connected to one or more controls and instruments for enabling workers in the enclosure 60 to monitor and control steam output. A steam output line 168, which is connected to the main steam line 158, conveys steam out of the control module 52 for subsequent use downstream in the SAGD system 20.

In use, the control module 52, the radiant module 54, and the convective module 56 are prefabricated separately. Prior to transportation, instruments and controls of the steam generator 22 are tested at the manufacturing site. More specifically, the testing involves testing communication between the instruments and the control system of the steam generator 22, which are housed in the enclosure 60, and testing the functionality of one or more of the instruments. For example, testing of pressure instruments involves a calibration that comprises an application of pressure and a resetting of zero and high range readings; testing of temperature instruments involves checking that ambient temperature is correctly measured, and confirming failure of each temperature instrument upon disconnection; testing of control valves involves auto-calibration of each valve, and stroking of each valve from the open position to the closed position; and testing of fire detection systems involves illuminating the interior space 66 with a high intensity light to simulate a fire. Other testing of instruments and controls is also carried out at the manufacturing site.

After testing, the control module 52, the radiant module 54, and the convective module 56 are each transported separately in a prefabricated state for installation at the operation site 24. Prior to installation, an array of steel piles 172, each in the form of a steel pipe having a square cap plate, is arranged in the ground at the operation site 24 to collectively provide a foundation 174. The control module 52 and the radiant module 54 are then each positioned onto a respective portion of the foundation 174, such that the skid 64 of the control module 52 and the skid 108 of the radiant module 54 each directly contacts ends of the piles 172. The skids 64 and 94 are then fastened to the piles 172 using one or more of bolts, rivets and welds. The convective module 56 is then installed on the radiant module 54, and the stack 138 is installed on the enclosure 136. Pipe connections and electrical connections between any of the control module 52, the radiant module 54, and the convective module 56 are made, as necessary.

As will be appreciated, the modular design of the steam generator 22 allows each of the control module 52, the radiant module 54 and the convective module 56 to be prefabricated at a location other than the operation site 24. As will be understood, this minimizes the amount of field work needed at the operation site 24, which advantageously reduces the cost associated with bringing the steam generator 22 to an operational status the operation site 24, as compared with conventional OTSGs. Additionally, the modular design of advantageously allows the steam generator 22 to be rapidly brought to operational status, enabling the steam generator 22 to be used for production more quickly than conventional OTSGs.

As will be appreciated, the prefabricated enclosure 60 of the control module 52 advantageously eliminates the requirement to construct a separate enclosure housing instruments and controls at the operation site, as would otherwise be required for conventional OTSGs. As will be understood, this feature reduces the cost and time associated with installation of the steam generator 22 at the operation site, which allows the steam generator 22 to be used for production more quickly and at a lower installation cost as compared to conventional OTSGs.

Additionally, and as will be appreciated, the prefabricated nature of the enclosure 60 of the control module 52 allows instruments and controls of the steam generator 22 to be tested at the manufacturing site prior to shipping and installation at the operation site. As will be understood, this ability to pre-test the instruments and control systems further reduces the cost and time associated with installation of the steam generator 22 at the operation site, which allows the steam generator 22 to be used to generate oilfield production more quickly and at a lower installation cost as compared to conventional OTSGs.

As will be appreciated, the “winterization” comprising the electrical heating elements 162 and thermal insulation layer 166 allow each of the main feed water supply line 128, the first and second feed water supply lines 132 and 134, the first and second preheated water lines 142 and 144, first and second steam output lines 152 and 154, the steam output line 156 and the main steam line 158 to be located externally of the enclosure 60. As will be understood, this eliminates the need to provide an enclosure having what would otherwise be a very large footprint around one or more of lines 128, 132, 134, 142, 144, 152, 154, 156 and 158 to provide “winterization” (namely, protection against freezing) of these external lines.

Additionally, and as will be appreciated, the steel frame structure of steam generator 22 allows the skids 64 and 94 to be supported directly by steel piles 172. As will be understood, the steel piles 172 may simply be driven to various depths as needed to compensate for any uneven grade, so as to provide a foundation 174 that is level. This feature advantageously enables the steam generator 22 to be installed in a quick and facile way on ground that is not uniformly flat and without requiring excavation.

Additionally, and as will be understood, the modular design of the steam generator 22 has a small footprint, which advantageously eliminates the need for concrete foundations that are otherwise required to support conventional OTSGs having large, field-erected enclosures. For example, FIG. 11 shows a conventional once-through steam generating system 500 that comprises a pair of conventional OTSGs partially housed in a field-erected enclosure 501 which, owing to the large size and the non-modular design of the conventional OTSGs, is required to be supported by a conventional concrete foundation 503. As will be appreciated, such conventional concrete foundations 503 are costly, and require additional resources in the field to produce. Additionally, the field-erected enclosure 501 includes field-erected enclosure extensions 505 that extend along the sides of radiant chambers 507 of the conventional OTSGs. The field-erected enclosure extensions 505 are otherwise required to provide protection against freezing to water lines (not shown) and steam lines (not shown) that extend partially the lengths of and external to the radiant chambers 507, and which each also require a respective portion 509 of the conventional concrete foundation 503.

Although in the embodiment described above, the enclosure 60 has a removable panel 102 disposed on a wall facing the radiant module for allowing the burner 90 to be accommodated in the interior space 66, in other embodiments, the enclosure may have other provisions. For example, in other embodiments, the enclosure may alternatively be provided with a hinged door, or simply an opening or other aperture. Still other arrangements may alternatively be used.

Although embodiments have been described above with reference to the accompanying drawings, those of skill in the art will appreciate that variations and modifications may be made without departing from the scope thereof as defined by the appended claims. 

1. A once-through steam generator for use at an oilfield operation site, the steam generator comprising: a control module supported by a first steel frame and having an enclosure comprising controls for operating the steam generator, the enclosure being erected prior to transportation to the operation site; a radiant module supported by a second steel frame and comprising a radiant chamber having a burner installed at an end thereof, the burner being configured to provide a heat transfer of between about 80 million Btu/h and about 200 million Btu/h; a convective module comprising an economizer heat exchanger, and wherein the radiant module supported by the second steel frame is transportable separately from the control module supported by the first steel frame.
 2. (canceled)
 3. The steam generator of claim 2, wherein the enclosure is configured to accommodate the burner.
 4. (canceled)
 5. The steam generator of claim 1, wherein the radiant module further comprises at least one water conduit and at least one steam conduit, said conduits being external to the radiant chamber.
 6. The steam generator of claim 5, wherein one or more of the conduits comprise: an electrical heating element disposed thereon, and a thermal insulation layer covering the conduit and the electrical heating element.
 7. (canceled)
 8. The steam generator of claim 1, wherein each steel frame is configured to be installed on a plurality of steel piles.
 9. The steam generator of claim 1, wherein each of the control module and the radiant module is installed on the respective steel frame prior to delivery to the operation site.
 10. The steam generator of claim 1, wherein the enclosure has an insulated interior sized to accommodate at least one worker.
 11. A method of installing a once-through steam generator at an oilfield operation site, the method comprising: providing each of: a control module supported by a first steel frame and having an enclosure comprising controls for operating the steam generator, the enclosure being erected prior to transportation to the operation site, a radiant module supported by a second steel frame and comprising a radiant chamber having a burner installed at an end thereof, the burner being configured to provide a heat transfer of between about 80 million Btu/h and about 200 million Btu/h, a convective module comprising an economizer heat exchanger, wherein the radiant module supported by the second steel frame is transportable separately from the control module supported by the first frame; and installing the control module, the radiant module and the convective module at the operation site.
 12. The method of claim 11, wherein said providing further comprises: transporting each of the control module, the radiant module and the convective module to the operation site.
 13. The method of claim 12, further comprising, prior to said transporting: testing said controls for operating the steam generator.
 14. The method of claim 11, further comprising, prior to said installing: forming a foundation in ground at the operation site.
 15. The method of claim 14, wherein the foundation comprises an array of steel piles. 